1. Field of the Invention
The present invention relates to an ink jet printing apparatus, and in particular, to an ink jet printing apparatus comprising a configuration that performs suction recovery on an ink jet print head.
2. Description of the Related Art
Printing apparatuses provide print output functions for printers, copiers, facsimile machines, and the like and are used as output instruments for composite electronic instruments and workstations including computers, work processors, and the like. The printing apparatuses print images on print media, for example, sheets or thin plastic sheets, on the basis of image information. The printing apparatuses can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and the like according to the printing scheme of the apparatus.
The ink jet printing apparatus uses a print head to eject ink to a print medium for printing. During a continuous operation of ejecting ink from the print head, normal printing may be prevented by dried ink in ink ejection ports in the print head or foreign material attached to the periphery of the ink ejection ports. Some ink jet printing apparatuses allow ink cartridges with ink filled therein to be separated from the print head. The type of ink jet printing apparatus needing only the replacement of the ink cartridge when the ink in that ink cartridge is exhausted requires a process for feeding ink into the print head after a new ink cartridge has been installed. Moreover, parts such as ink paths and ejection ports through which ink flows constitute very small spaces. Bubbles may be collected in paths or communication sections through which ink flows from ink tanks to ink nozzles. The bubbles need to be removed.
Thus, the ink jet printing apparatus comprises a recovery mechanism allowing negative pressure to act on the interior of a cap covering an ejection port surface of the print head to suck and forcibly discharge ink from the print head. This enables dried ink, foreign material, air, and the like to be discharged together with the ink and also allows ink to be introduced after the appropriate ink cartridge gas been replaced. Bubbles in the ink paths and the like can also be discharged. Another known recovery process is an ejection operation unrelated to printing and performed at a predetermined position in the cap (this operation is hereinafter also referred to as preliminary ejection). In this recovery process, waste ink discharged into the cap is accommodated in the cap under the same action as that of the suction.
A known source for negative pressure for the suction recovery process uses a tube pump. The tube pump externally controls a tube using a plastic member and internally has a rotating shaft comprising a roller that rotatably presses the tube. Rotating the rotating shaft rotates the roller in conjunction with the rotating shaft while pressing the tube, to generate negative pressure. The negative pressure reduces the pressure on an ink ejection port surface of the ink jet print head to recover ink suction. To recover suction using the tube pump, the negative pressure in the cap is increased while sucking ink. Thus, before the pressure on the ejection port surface decreases to a desired value, more ink than required may be discharged from the print head.
That is, the amount of ink sucked to fill ink into an ink path 302, an ink common liquid chamber 303 and the like in the print head shown below in FIG. 7 can be easily set. However, the negative pressure in the cap needs to be further increased in order to remove bubbles from very small parts such as the bubbling chamber 308 and the like in the ink ejection nozzle section. Thus, even after the ink is filled into the ink path 302 and the ink common liquid chamber 303 the ink may need to be further sucked.
Another known form of negative pressure source uses a piston pump. For example, a piston is provided in a closed cylinder in tight contact with an inner wall thereof so as to prevent pressure leakage. The piston is then moved to reduce the pressure of the interior of the cylinder. Subsequently, once the piston passes through a hole that is in communication with the ejection portion surface of the ink jet print head, the negative pressure in the cylinder is transmitted to the ink jet print head to recover ink suction.
To perform suction recovery using the piston pump, an initial negative pressure can be set at a large value. That is, the suction pressure required to remove bubbles from very small parts such as the bubbling chamber 308 and the like in the ink ejection nozzle section can be set with comparative ease. However, it is difficult for the piston pump to adjust the amount of ink to be filled into the ink path 302, the ink common liquid chamber 303 and the like owing to the difficulty with which the suction amount is varied as well as a narrow adjustment range. Accordingly, a suction operation for filling ink into the ink path 302, the ink common liquid chamber 303 and the like needs to be performed a number of times to adjust the suction amount.
As describe above, the above pump fails to optimization the suction recovery for filling ink into the ink path 302, the ink common liquid chamber 303 and the like, and the suction recovery for removing bubbles from the bubbling chamber 308 and the like in the ink ejection nozzle section. That is, the problem of reduction of the amount of sucked while maintaining the reliability of a print head remains.
In contrast, Japanese Patent Laid-Open No. 09-323432 discloses a recovery process using a tube pump wherein a valve is placed in a configuration for suction recovery to increase the negative pressure. Japanese Patent Laid-Open No. 2000-52568 discloses a recovery process also using a tube pump wherein a valve is placed in a configuration for suction recovery to increase the negative pressure, enabling two-step suction.
According to the recovery process described in Japanese Patent Laid-Open No. 09-323432, the valve is placed in the configuration for recovery to increase the negative pressure, so that a high negative pressure acts rapidly to increase the speed at which ink is discharged, enabling bubbles to be removed from the ink paths and the like. However, the high negative pressure dose not enable to be kept for a long time, the suction for removing bubbles under the high negative pressure dose not enable to be apply to the ink suction for filling ink into the print head. Further, if two-step suction is performed first under a low pressure and then under an increased pressure using the recovery process described in Japanese Patent Laid-Open No. 2000-52568, the pump operates even during the pressure switching operation, preventing a reduction in the amount of ink sucked.